For example, in a double-sided copper-clad laminated plate for a printed wiring board (referred to as “glass epoxy copper-clad laminated plate” below) formed of glass fiber base material epoxy resin, wirings formed on both sides are normally connected with a through hole. Specifically, for example, the through hole can be obtained by forming a copper layer on an inner wall of the through-hole by using an electroless plating method and an electrolytic plating method after the through-hole has been formed in the glass epoxy copper-clad laminated plate on the basis of drill processing.
Regarding a request for mounting minute components with high density, the glass epoxy copper-clad laminated plate has poor dimensional stability. Although there is a double-sided copper-clad laminated plate for a printed wiring board with excellent dimensional stability, that is expensive. Therefore, for example, amounting substrate using a glass substrate having a thickness equal to or less than 0.5 mm has been considered. However, it is difficult to form a copper layer on the inner wall of the through-hole on the basis of the electroless plating method with good adhesion after the through-hole has been formed in the glass substrate. Instead of the electroless plating method and the electrolytic plating method, a method for filling the through-hole by using conductive paste is disclosed, for example, in Japanese Patent Application Laid-Open No. 2002-324958.
When the component is mounted on the mounting substrate, a component mounting method is often employed for melting a solder layer and mounting the component to the component attaching part via the solder layer after the solder layer has been formed on the component attaching part where the component is mounted, and subsequently, the flux has been coated. In general, the flux is partially coated to a desired position by using a printing method and the like. However, a position accuracy of the pattern formed in this way has a large tolerance of about a few dozen μm. When a connection pitch gets smaller to a few dozen μm, it is difficult to apply this method. Therefore, as a solution, a method for coating the flux to the entire surface is employed, for example, as disclosed in Japanese Patent Application Laid-Open No. 2010-123780.